While other illicit drug use continues to decline in the 1990s, LSD (lysergic acid diethylamide) is a notable exception. The reemergence in the 1990s of this largely forgotten drug from a previous era has reignited old fears and sparked new waves of legal repercussions. Recent problematic developments (increases in: prevalence of use, especially among youth; emergency-room admissions; use in combination with other drugs; arrests) have accompanied the increased popularity of LSD within diverse social worlds and contexts of use. Other psychedelic drugs such as psilocybin ("magic mushrooms") and MDMA ("ecstasy") appear to be attracting new users with their growing reputations as gentler, less threatening alternatives to LSD. Efforts to formulate an appropriate response to increasing psychedelic-drug use remain severely hampered by our lack of knowledge concerning contemporary use of these substances. Given the virtual absence. of sociological research on psychedelics over the past two decades, this exploratory study proposes to employ a largely qualitative methodology to understand current psychedelic drug-use patterns and its concomitant problems. New groups of people are using psychedelic drugs, and the diversity of contexts in which these drugs are being used is increasing. We will identify these user groups and contexts of use and interview samples of users. By combining extensive ethnographic fieldwork with 200 in-depth user and 75 "community consultant" interviews, our findings will help to address the substantial gaps in knowledge about contemporary psychedelic use. Our overall objectives and specific aims are guided by the need to carefully examine the respective and interactive roles played by pharmacology (drug), user groups (set), and contexts (setting) in shaping current patterns and problems associated with the use of LSD and other psychedelic drugs.